// T94 

// 递归中序遍历
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
 var inorderTraversal = function(root) {
  const res = []
  const rec = (node) => {
      if (!node) return
      rec(node.left)
      res.push(node.val)
      rec(node.right)
  }
  rec(root)
  return res
};

// 迭代
var inorderTraversal2 = function(root) {
  const res = []
  const stack = []
  let p = root
  while (stack.length || p) {
      while(p) {
          stack.push(p)
          p = p.left
      }
      let n = stack.pop()
      res.push(n.val)
      p = n.right
  }
  return res
};